Method of inhibiting corrosion



United States Patent 3,288,555 METHOD OF INHIBITING CORROSION Donald R. Napier and Olen L. Riggs, Jr., Ponca City, Okla., assignors to Continental Oil Company, Ponca City, Okla., a corporation of Oklahoma No Drawing. Filed Feb. 5, 1965, Ser. No. 430,747 18 Claims. (Cl. 212.7)

The present invention relates to an improved class of corrosion inhibitors. More particularly, the present invention relates to a method of inhibiting corrosion of metal surfaces due to mineral acids by the use of certain surface active quaternary ammonium compounds as the corrosion inhibitor. In one aspect, the present invention relates to a method of preparing certain surface active quaternary ammonium compounds.

Numerous materials are known which are useful in varying degrees as inhibitors for the corrosion of metal surfaces, and particularly ferro-metallic surfaces, due to contact with mineral acids. Many inhibitors are considered satisfactory for their intended use, nevertheless it is readily apparent that the need is ever-existent for'a corrosion inhibitor which is more effective and/or less expensive. Thus, it is highly desirable to produce a corrosion inhibitor which is more effective than, or equally eifective at lower concentration than, the inhibitors of the prior art. The present invention is concerned with such a class of inhibitors.

The prior art recognizes that quaternary ammonium compounds have been suggested as inhibitors for the corrosion of metal surfaces. R. J. Meakins in the Journal of Applied Chemistry (13, August 1963) teaches that nalkyl quaternary ammonium compounds are useful as inhibitors of the acid corrosion of steel. This article particularly teaches that n-hexyldecylpyridinium bromide is useful as a corrosion inhibitor. According to the present invention we have found, unexpectedly, that the use of an alkyl aromatic radical in place of an alkyl radical in the quaternary-ammonium compound gives a pronounced improvement in the rate of inhibition of acid corrosion of a metal surface, particularly a ferro-metallic surface.

It is an object of the present invention to provide an improved class of corrosion inhibitors.

-It is another object of the invention to provide a corrosion inhibitor composition for use in inhibiting corrosion of ferro-metallic surfaces due to contact with mineral acids which is more effective than the compositions of the prior art.

' -It is still another object of the invention to provide a more. effective method of inhibiting corrosion of metallic surfaces, and particularly ferro-metallic surfaces, due to contact with mineral acids by the use of a surface active quaternary ammonium compound, containing an alkaryl radical, as the inhibitor.

It is a particular object of the invention to "provide a more effective method of inhibiting vacid corrosion of ferro-metallic surfaces by theme of a surface active quaternary ammonium compound prepared by reacting a halomethylated alkyl-aromatic compound with a heterocyclic nitrogen-containing compound, such as 2-picoline or quinoline.

It is yet another object of the invention to'provide a method of preparing certain surface active quaternary ammonium compounds which are useful in inhibiting corrosion .of metallic surfaces due to contact with mineral acids.-

It is a further object of the invention to provide a method of preparing poly halomethylated surface active alkylaromatic compounds which are useful in preparing the aforementioned surface active quaternary ammonium compounds.

ice

Broadly stated, the present invention resides in the discovery that certain surface active quaternary ammonium compounds have an unexpectedly improved efiicacy as an inhibitor to prevent the corrosion of metals due to contact with mineral acids. The quaternary ammonium compounds of our invention, generically, are represented by the formula:

wherein R is an alkyl group, straight or branched chain, having from about 8 to about 22 carbon atoms, preferably from about 9 to about 15 carbon atoms; Ar is an aromatic hydrocarbon radical, preferably derived from benzene or naphthalene; A is an organic nitrogen radical containing one or more double-bonded, conjugated nitrogen atoms; X is a halogen atom, preferably chlorine or bromine; n is a number in the range of about 1 to about 3, preferably in the range of above about 1.5 to less than about 2.5.

The corrosion inhibitors of our invention are prepared by reacting a halomethylated alkyl aromatic compound with a double-bonded, conjugated nitrogen compound.

A suitable alkyl aromatic compound which can be halomethylated and then reacted with the nitrogen compound has the following formula:

wherein R is a normal or branched-chain aliphatic radical containg from about 8 to about 22 carbon atoms, preferably from about 9 to about 15 carbon atoms, R R and R are either hydrogen, methyl or ethyl.

Similarly, substituted polynuclear aromatic hydrocarbons are also suitable, but to a lesser degree than the material described above. These materials have the formula:

wherein R R R and R are as defined above.

It is to be understood that mixtures of the ab ovealisted materials can be used to prepare the corrosion inhibitors of our invention. In fact, the commercially available alkyl-aromatic hydrocarbons for use in our invention usually are mixtures of these materials.

An example of a particularly suitable commerciallyavailable alkyl aromatic hydrocarbon which can be used to prepare the corrosion inhibitor of our invention is a material which is known to the trade as dodecylbenzene. Dodecylbenzene is available under the trade name of Neolene 400 from Continental Oil Company. In a typical process dodecylbenzene' is prepared by firstpolymerizing propylene to produce a mixture of olefins which are predominantly C (dodecene). The dodecene is than alkylated with benzene to produce dodecylbenzene, The preparation of dodecylbenzene is described more completely in US. Patent 2,941,015 to Robert R. Ky-

' lander, which patent is made a part of this specification.

- 3 A typical sample of dodecylbenzene has the following properties.

Distillation Range, F.:

I.B.P. 535 545 550 50% 560 90% 580 97% 592 F.B.P. 603 Percent recovery -5 99 Specific gravity, 60 F. 0.875 Molecular weight 1 237 Aniline point 2 48.5 Bromine No. 3 0.12 Saybolt color 4 29 Refractive index, 25 C 1.4885 Appearance, clear and water white.

Flash point (closed cup), F. 5 260 Viscosity, centipoises At 68 F 14 At 32 F 37 1 Cryoscopic method using benzene. ASTM D-G ll,

3 ASTM D-1159.

4 ASTM D-156.

5 ASTM D-56.

It is generally known that the alkyl group in dodecylbenzene is branched chain. More recently, in order to produce detergents which are less resistant to attack by bacteria, straight chain alkyl aromatic hydrocarbons, similar to dodecylbenzene, have been prepared. These materials constitute a class of materials which, when sulfonated, are known in industry as biodegradable detergents. It is to be understood that any of the n-alkyl aromatic hydrocarbons which are used in preparing biodegradable detergents can be used to prepare the corrosion inhibitors of our invention.

The preparation of a particularly suitable n-alkyl aromatic hydrocarbon for use in our invention is described in application Serial No. 129,252, filed August 4, 1961, and now abandoned, and having the same assignee as the present application. For reason of convenience, this application is made a part of the present application. Briefly, application Serial No. 129,252 relates to a process of preparing a detergent alkylate wherein the process comprises the following steps, broadly stated: (a) separating a fraction of substantially straight chain C -C hydrocarbons from a petroleum distillate substantially free of olefins and containing 'said straight chain hydrocarbons together with non-straight chain hydrocarbons, (b) chlorinating said fraction to the extent whereby between about 10 and about 35 mole percent of the straight chain hydorcarbons present are substantially only mono-chlorinated, (c) alkylating an aromatic compound, selected from the group consisting of benzene, a lower alkyl substituted benzene and mixtures thereof, with the chlorination product of step (b) in the presence of an alkyl'ation catalyst.

n-Alkyl aromatic hydrocarbons of the aforementioned type are available under the trademarks Nalkylene 500 and N-alkylene 600 from Continental Oil Company. These materials have the following typical properties:

NALKYLENE 500 The alkyl aromatic hydrocarbon can be subjected to varying degrees of halomethylation. In fact, usually the halomethylation products are mixtures of products containing 1, 2 or 3 halomethyl groups. The degree of halomethylation is the average of the number of halomethyl groups present. For convenience in describing the halomethylation products we have adopted the following terminology: the term mono refers to those materials having from about 1 to less than about 1.1 halomethyl groups; the term poly refers to those materials having from about 1.1 to about 3 halomethyl groups; the term bis refers to those materials having above 1.5 and less than 2.5 halomethyl groups. Since in certain instances the bis halomethylated derivatives provide superior results, the inhibitors derived from this material are preferred.

Also, the term halomethylation as used herein refers only to either chloromethylation or bromomethylation.

Suitable double-bonded, conjugated nitrogen compounds are the following:

Pyridine Lower monoalkyl (C and C 2-substituted pyridines,

such as Z-picoline and 2-ethylpyridine Lower dialykyl (C and C 2,3; 2,4; and 2,5-substituted pyridines, such as 2,4-lutidine, 2,5-lutidine, 2,6-lutidine,

Z-methyl-3-ethylpyridine, 2-methyl-4-ethyl-pyridine, 2-

ethyl3-methylpyridine, 2-ethyl-4-methylpyridine, and

2-ethyl-5-methylpyridine Lower trialkylpyridines having either the 2 or 6 positions (but not both) open, such as 2,3,5-trimethylpyridine,

and 2,3,5-triethyl-pyridine Polynuclear heterocyclic nitrogen compounds, such as quinoline, isoquinoline, benzoquinolene phenanthridine and acridinef *While the materials marked with an asterisk are suitable, 'they are less suitable, because of low reactivity, than the other materials listed herein.

Many of the commercially available nitrogen compounds suitable for preparing the corrosion inhibitors Of our invention are mixtures of the above-described material-s. 'Ilhese materials are available from the following companies under the following names.

Reilly Ta-r and Chemical Co.:

LAP HAP Allied Chemical Company:

Tar Base Inhibitor Base Quinoline Residue Koppers Company:

15-18 grade base 16-20 grade base Wet pr ng high boiling base The name LAP above refers to low-boiling alkylpyridmes, havln g the following properties: i

Distillation range at 760 mm., 5-95%, C 172-183 The name HA above refers to high-boiling alkylpyri dines, having the following properties:

Distillation range at 760 C. 2% 204 Decomposition after 80% distilled:

Density at 20 C. 'g./rnl 1.003 Neutral oil, percent 8.6 Approximate equivalent weight 200 Specific examples of the materials which are suitable as corrosion inhibitors in our invention are given below. The nomenclature employed is as follows. The hydrocarbon part of the molecule is given first. The degree of halomethylation is indicated by a subscript. Finally, the nitrogen compound used to form the quaternary is indicated.

n Arlkyl benzene (CH Cl) apyridine n-Alkyl benzene (CH Cl) -2-picoline n-Alky1(c 22) benzene 2,4-lutidine n-Al kyl benzene (CH Cl) 2,5-lutidi-ne n-Allcyl benzene (CH Cl) -2-methyl-5-ethyl pyndme n-Alkyl benzene (CH Cl) -2-ethyl-4-methyl ridine 11-Alkyl benzene (OH Cl) -quinoline u-Alkyl benzene (CH Cl) -isoqu-inoline br-Alkyl benzene (CHgBr) -2-rmethyl-5-ethyl pyrid-me br-Alkyl(cg cgg) benzene (CH Br) -2-cthyl- 4-met.'hyl

ridine br-Alkyl benzene (CH Br) -isoquinolrne br=branched chain.

The first step in preparing the surface-active quaternary ammonium compounds, which are usefiul as corrosion inhibitors in our invention, is the preparation of the polyhalomethylated al-kyl aromatic hydrocarbon (preferably polychloromethylated alkyl aromatic hydrocarbon). The preparation of these materials uses a particular chloromethylating agent which is formed by reacting tfiormaldehyde or a compound which engenders formaldehyde with a chlorinecontaining compound which will engender hydnogen chloride in the presence of an alcohol and sulfuric acid.

Suitable chlorine-containing compounds which will engender hydrogen chloride under the conditions used herein include phosphorus trichloride, phosphorus pentachloride, sulfuric oxychloride, sulfurous oxychloride, and acyl chlorides such as acetyl chloride.

Suitable alcohols are the primary monatomic saturated aliphatic alcohols containing from 1 to 4 carbonatoms, such as, for example, methanol, ethanol, normal propanol and normal butanol.

The relative amounts of the various components of the chloromethylating reagent, and the amount of chloromethylating agent used in relation to the alkaryl hydrocarbon, are shown below.

The chloromethylation reaction is conducted at a temperature in the range of about 65 to about 70 C., preferably about 66 to about 68 C., and for .a time in the range of from about 3 to about 7 hours, preferably [from about 4 to "about 6 hours.

Specifically, the chloromethylation procedure can be. illustrated as follows: 200 grams of dodecyllbenzene :is treated with a chloromethylating mixture which has been prepared as follows: 42 grams of a p-fonmaldehyde and 43 grams methyl alcohol are added to a 1-liter Morton flask which is equipped with a sealed stirrer, thermometer, and dropping tunnel. The iiask is placed in an ice bath and 65.5 grams of phosphorus tri-ohloride are added to the dropping funnel. Mixing is begun. The phosphorus trichloride is added dropwise while maintaining the temperature between and F. After the chloride addition, the reaction mass is aged 10 minutes at the same temperature. 175 grams of percent sulfuric acid is then added to the dropping funnel. The sulfuric acid is then added to the reaction mass at a rate which permits a constant temperature to be maintained. This is followed by post-stirring the reaction mass for an additional 15 minutes. This reaction mass and the dodecyibenzene are combined and heated at 52-57 C. for 3 hours to produce the chloromethylated dodecylbenzene.

It is of interest that using a normal alkylbenzene as the starting material and the preferred condition .described above results in a product containing similar amounts of mono and tris chloromethylated alkylbenzenes. By contrast, under the same conditions usinga branched alkylbenzene (e.g., commercial dodecylbenzene) results in a product containing mostly bis chloromethylated alkylbenzenes.

The quaternary corrosion inhibitor is prepared from the nitrogen compound and the chloromethylated alkyl aryl hydrocarbon as follows: .lpart of chloromethylated alkyl aryl hydrocarbon-nitrogen compound (10 percent excess) mixture and 1 partof isopropanol are added to a reaction vessel. The reaction mass is heated at reflux for from 3 to 6 hours.

While the corrosion'i'nhibitors of our invention can be used to inhibit'the attack'of any mineral acid on metallic surfaces, preferably, they are used to inhibit the attack due to hydrochloric or sulfuric acid. Also, preferably the metallic surface is a ferro-metallic surface. Usually, inhibitors are used in connection with dilute acids. However, it is within the scope of our invention to use the corrosion inhibitors in either hydrochloric or sulfuric acid in all concentrations which are commercially available.

The inhibitors of our invention are suitable when used in a concentration as low a 0.0010 percent (weight). Usually, and more suitably, the concentration of in hibitor will be at least about 0.0050 percent (weight). Preferably, the inhibitor is present in the acid medium in an amount of at least about 0.0200 percent (weight). It is well recognized that economics dictate the upper limit of the amount of inhibitor employed. Preferably, the inhibitor is not used in an amount above about 0.50 percent (weight) and usually it is never used in an amount above about 5.0 percent (weight).

The corrosion inhibitor is suitable for use in any of the environment wherein corrosion inhibitors are employed to prevent attack of mineral acids on metallic surfaces. One such use for which our inhibitor is particularly effective is in the prevention of corrosion in pickling baths. Another use for our inhibitor is the acidizing of oil bearing structures wherein corrodible equipment is involved.

In order to disclose the nature of the present invention still more clearly the following illustrative examples will be given. It is to be understood, however, that the invention is not to be limited to the specific conditions or details set forth in these examples except insofar as such limitations are specified in the appended claims. Parts given are parts by weight.

EXAMPLE I Thi example illustrates the preparation of a typical corrosion inhibitor of our invention.

A. Preparation of 3,4-bis(chloromethyl)dodecylbenzene A 2-liter Morton flask equipped with stirrer, thermometer, reflux condenser and addition funnel was charged withformaldehyde (168 parts) and methanol (172 parts). With cooling applied to the flask, phosphorous trichloride (262 parts) was added dropwise in 20 minutes, the temperature being maintained at 26 to 31 C. The mixture was post-stirred minutes, then 100 percent sulfuric acid (700 parts) was added in 25 minutes, while maintaining the same temperature. After post-stirring the chloromethylating mixture for 22 minutes, DBCl (pri marily 4-chloromethyl dodecylbenzene, 480 parts) was charged to the flask and the resulting mass was stirred and heated at 75 C. for 3 hours.

The mass was allowed to settle overnight. The upper (organic) layer was separated and then recycled to a second chloromethylation treatment identical to the first. Analyses indicated that the final product contained approximately 80 mole percent of the 3,4-bis chloromethyl derivative. After washing withhot water, followed by hot 2 percent sodium carbonate, and filtering through Hy-Flo filter aid, the product was subjected to fractional distillation. A viscous, colorless fraction containing 19.9

weight percent benzyl-type chlorine and some 90.6 mole percent of the 3,4-bis derivative was isolated.

(B) Preparation of the pyridinium derivative of a his chloromethylated dodecylbenzene The 91 percent bis chloro compound (2.0 parts) described above, pyridine (0.975 parts10 percent stoichiometric excess) and isopropanol (2.8 parts) were stirred and heated at reflux for 2 hours. The product was a homogeneous liquid containing *(i2) percent of the theoretical amount of chloride ion. It dissolved in water to give a soapy, oil-free, light amber-colored solution.

TEST CONDITIONS Testing was conducted in controlled temperature baths maintained at F. and F. Steel coupons were cut from Az-inch thick sheets of steel. The steel used in the test was S.A.E. 1020 mild steel, 302 stainless steel, and a low-chromium alloy steel (-2% Cr). (Unless otherwise noted the steel employed was S.A.E. 1020 mild steel.) The steel coupons were surface ground, cleaned in acetone to remove grease and solvents, and weighed. Bottles of approximately 300 ml. capacity were filled with test solution (10 percent HCl, or 5 percent H 80 plus 0.5 percent NaCl) and brought to temperature. The inhibitors were then added to the desired concentration and the coupon was immersed.

Corrosion rates were obtained both by measuring the hydrogen evolved by the corrosion reaction and by Weighing the coupon after specified time intervals. Rates were determined in both inches penetration per year (ipy) and pounds of steel dissolved per 1000 square feet per hour. Most tests were carried out in duplicate, although occasionally triplicate and quadruplicate tests were conducted. Corrosion rates given in the tables are averages of the multiple tests conducted. Percent inhibition, where given, is defined as:

Uninhibited Rate-Inhibited Rate Uninhibited Rate EXAMPLE II TABLE I" [Corrosion Rates in 10% HCl at 180 F.: Comparison of Br-alkylbenzene 2 (CHzCl)1. Quinoline to Commercial Material (M 1 Initial Rates, #/1000 itJ/hr. Initial Rates, i.p.y. Percent Protection Inhibitor Concentration p.p.m.

Quaternary Commercial Quaternary Commercial Quaternary Commercial Material A Material A Material A 1 Corrosion rates change continuously over a long term test due to inhibitor breakdown. Rates in this table are average rates over the first hour.

Data on rates at other time appear in Table 3 Rodine 213.

a EXAMPLEIII Using the procedure described above, the corrosion rates in percent HCl at 140 F. of two quaternarynitrogen compounds of our invention were determined and compared with commercial material A.

compounds are identified in Table III below, wherein the results of this example are shown.

For purposes of comparison the results obtained on commercial material A are included.

The inhibition percentages were obtained from weight losses after 6 hours in uninhibited and inhibited HCl at TABLE III [Inhibition Levels 1 Obtained on a Series of N -alkylbenzene Quaternaries of Various Aromatic Amines] Inhibitor Concentration, p.p.m., percent Aromatic Amine 16-20 Base 94. 1 99. 4 99. 7 99.7 99. 8

Commercial m 84. 5 87. 7 98. 4 99. 5 99. 7

1 Defined in Example IV, above. 2 Commercial coal tar base described previously. 3 Commercial coal tar base described previously. 4 Commercial coal tar base obtained from Koppers Company. 5 Commercial coal tar base obtained from Koppers Company.

The quaternary-nitrogen compounds were the following:

Quat 1=n-alkylbenzene (-CH Cl) alkyl pyridine Quat 2=n-alkylbenzene (CH Cl) quinoline The n alkylbenzene used was Nalkylene 500, described previously.

The alkyl pyridine used was "15-18 base obtained from Koppers Company.

" The results of this example are shown in Table II below.

Inspection of the table shows that the quaternary compounds of our invention are superior.

TABLE II EXAMPLE v [Corrosion Rates in 10% HCl at 140 F: Comparison of Two Quaternaries to Commercial Material A] 7, Initial Rates, ti /1,000 itJ/hr. Percent Protection Inhibitor Concentration p.p.m.

t. 1 net. 2 Commercial Quat. 1 Quat. 2 Commercial Qua Q Material A Material A A LE IV The results of this example are shown in Table IV,

In this example inhibition level-s were determined on a series of quaternary-compounds derived from chlorobelow.

Inspection of the table shows that our corrosion inhibitors are superior.

TABLE IV [Inhibition Levels 1 Obtained on Two Quinoline Quaternaries and Two Commercial I Inhibitors in H 80 t i Inhibitor Concentration, p.p.m.

- r Material Tested Br-alkylbenzene T (OH CD quinoline 99.6 99.7 99.9 99.8 99.8 99.8 n-Alkylbenzene (CHzCl) .5 quinoline 99.5 99.8 99.9 99.9 99.9 99.9 K Commercial material B 97. 4 97.8 97. 9 98. 6 98. 6 98. 6 Commercial material A 98.8 99.5 99. 8 99. 8 99. 8 99.9

1 As in Table III.

2 The br-alkylbenzene was "Neoline 400 a commercial dodecylbenzene. 8 The n-alkylbenzene was Nalkylene 500, described previously.

methylated n-allcylben zene and various heterocyclic nitrogen compounds. -The n-a-lkylbenzene was Nalkylene 500, described previously. The heterocyclic nitrogen EXAMPLE VI This example illustrates the improved stability of our corrosion inhibitors. The procedure used was essentially that used previously, with the exception that a measurement was made of the time necessary for the degree of protection, afforded by the inhibitor, to drop the specified levels (90% and 99%).

The quinoline derivative of chloromethylated branched dodecylbenzene (same as used in Example II) was cm pared against commercial material A.

The results of this example are shown in Table V, below.

Inspection of the table readily shows the superiority with regard to high temperature stability of our corrosion inhibitors.

This example illustrates the improvement provided by the quaternary compounds derived from an alkaryl hydrocarbon of the subject invention when compared to a quaternary compound, derived from an alkyl hydrocarbon, of the prior art.

The testing procedure was the same as that used in Example II.

The material of our invention which was tested was bralkylbenzene (CH CD pyridine. The alkaryl hydrocarbon portion of this compound was described in Example H.

The material of the prior art was n-hexadecylpyridinium bromide.

To extend the comparison, data was obtained on nhexadecylpyridinium chloride.

The results of this example are shown in Table VI, below.

Inspection of this table shows that substitution of an alkaryl radical for an alkyl radical gives a several-fold improvement in corrosion rate at lower concentrations.

TAB LE VI [Corrosion Rates and Protection Levels for Simple n-alkyl Quaternaries Compared to an Alkaryl Quaternary of Our Invention] Inhibitor Conccntra- Corrosion Percent tion, p.p.m. Rate, i.p.y. Inhibition n-Hcxadecylpyridininm bromide 200 1.95 89. 500 1. 40 92. 5 1, 000 1. 02 94. 5 n-Hexadecylpyridinium chloride 200 0. 88 95. 3 500 0. 60 96. 8 V 1 1, 000 0. 37 98. 0 r r hi d 1 20 s 16 as o ri ine a 1 a DY 100 1.00 94. 6 200 0. 26 98. 6 500 0. 41 97. 8 1, 000 0. as as. 2

' 1 This material is a relatively pure mono product (1.04 CHzCl units/ aromatic nucleus).

l 2 EXAMPLE VIII This example illustrates the improvement provided by bis-chloromethylated derivatives as compared to monochloromethylated derivatives.

The test procedure was the same as in Example 11.

The mono-derivative was br-alkylbenzene (CH CD pyridine; whereas the bis-derivative was br-alkylbenzene (CH2C1) g4 pyridine.

The results of this example are shown in Table VII, below.

TAB LE VII [Comparison of Mono-chloromethylated to Bis-chlorornethylated Pyridine Based Quaternaries] Inhibitor Corrosion Rate, i.p.y. Percent Inhibition Concentration, p.p.m.

Mono Bis Mono Bis EXAMPLE IX This example provides a comparison of n-hexadecylpyridinium chloride and a quinoline quaternary derivative of bis-chloromethylated branched dodecylbenzene (derived from Neolene 400 and having a chloromethylation degree of 1.94).

The results of this example are shown in Table VIII below.

Inspection of thetable readily shows the superiority of the bis quinoline quaternary of our invention.

TABLE VIII Percent Protection Inhibitor Concentration,

p.p.m. Hexadecylpyridinium Bis DB 01* Qninoline Chloride quat. quat.

*Br-dodecylbenzene (CHzCDrM quinoline.

EXAMPLE X This example illustrates the corrosion inhibition provided by a typical inhibitor of our invention on additional types of steels. The inhibitor tested was a quinoline derivative of chloromethylated branched dodecylbenzene. The degree of chloromethylation was 1.56. The inhibitor was tested at a concentration of 200 p.p.m. in 10% HCl at F. The inhibitor gave a 99.9% protection on a low-chromium alloy steel (-2% Cr) and 99.6% protection on 302 stainless steel.

EXAMPLE XI This-example illustrates the chloromethylation of various alkaryl hydrocarbons, and monochloromethyl derivatives of various alkaryl hydrocarbons, employing the chloromethylating reagent described herein. The conditions of time and temperature are described in Table IX below, wherein. the results of this example are shown.

The br alkylbenzene was Ne0lene" 400, a commercial dodecylbenzene, described previously.

TABLE IX Quantity of Chloro- Reaction Run No. Starting Material methylating Temp. Time N I Reagent 0.) (hrs) (Units) Neolene 40D 4 2 67-70 1. 51 Dodecylben zyl chloride 2 65 1. 65 Dodecylbenzyl chloride 5 1 75 5 1. 42 Dodeeylbenzyl chloride 5 2 75 10 Nalkylene'500 2 67-70 5 1.53 Product of Example V 2 67-70 5 1. 95 Nalkylene 600 2 67-70 5 1. 32

1 A unit of reagent contained the following: 1.75 moles-formaldehyde; 1.63 moles-methanol; 0.60 mole-PO1 2.25 moles-sulfuric acid.

1 n refers to the degree of ehloromethylation of the alkaryl hydrocarbon, as defined previously.

3 No product could be isolated 4 Neolene 400 refers to a 5 Derived from Neolene liggnched-chain dodecylbenzene, described previously.

While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto, since many modifications may be made; and it is, therefore, contemplated to cover by the appended claims any such modifications as fall within the true spirit and scope of the invention.

The invention having thus been described, what is claimed and desired to be secured by Letters Patent is:

1. A method of inhibiting the attack of mineral acids on metal surfaces which comprises adding to the mineral acid an inhibiting amount of a surface active quaternary ammonium compound represented by the formula selected from the group consisting of hydrochloric acid and sulfuric acid.

3. The method of claim 2 wherein (l) the aromatic hydrocarbon radical is derived from benzene, and (2) the heterocyclic nitrogen radical is derived from a nitrogen compound selected from the group consisting of pyridine, 2-picoline, 2-etl1ylpyridine, 2,4-lutidine, 2,5-lutidine, 2,6- lutidine, 2-methyl-3-ethylpyridine, 2-methyl-4-ethylpyridine, 2-methyl-5-ethylpyridine, 2-ethyl-3-methylpyridine, 2-ethyl-4-methylpyridine, Z-ethyI-S-methylpyridine, 2,3,5- trirnethylpyridine, 2,3,5-triethylpyridine, quinoline, isoquinoline and mixtures thereof.

4. The method of claim 3 wherein the nitrogen compound is pyridine.

5. The method of claim 3 wherein the nitrogen compound is 2-picoline.

6. The method of claim 3 wherein the nitrogen compound is 2-ethy1pyridine.

7. The method of claim 3 wherein the nitrogen compound is quinoline.

8. The method of claim 3 wherein the nitrogen compound is isoquinoline.

9. A method of inhibiting the attack of hydrochloric acid on ferro-metallic surfaces which comprises adding to the hydrochloric acid an inhibiting amount of a surface active quaternary ammonium compound rep-resented by the formula wherein R is an alkyl group of from about 8 to about 22 carbon atoms, Ar is an aromatic hydrocarbon radical derived from the group consisting of benzene and naphthalene, A is a heterocyclic nitrogen radical containing a conjugated double bond, the radical being attached through the nitrogen atom to the remainder of the molecule, X is a halogen selected from the group consisting of chlorine or bromine, and n is a number in the range of about 1 to about 2.

10. The method of claim 9 wherein the surface active quaternary ammonium compound is used in an amount in the range of about 0.0010 percent (weight) to about 5.0 percent (weight).

11. The method of claim 10 wherein the aromatic hydrocarbon radical is derived from benzene.

12. The method of claim 11 wherein the heterocyclic nitrogen radical is derived from a nitrogen compound selected from the group consisting of pyridine, 2-picoline, 2-ethylpyridine, 2,4-lutidine, 2,5-lutidine, 2,6-lutidine, 2- methyl-3-ethylpyridine, 2-methyl-4-ethylpyridine, 2-methyl 5 ethylpyridine, 2-ethyl-3-methylpyridine, 2-ethyl-4- methylpyridine, 2-et-hyl-S-methylpyridine, 2,3,5-trimethylpyridine, 2,3,5-triethylpyridine, quinoline, isoquinoline, and mixtures thereof.

13. The method of claim 10 wherein the quaternary ammonium compound is a pyridinium derivative of chloromethylated dodecylbenzene, characterized further in that 1) the term pyridinium refers to derivatives of a mixture of pyridine and methyl-and-ethyl substituted pyridines, and (2) the dodecyl portion of said dodecylbenzene is a mixture of branched-chain alkyl groups containing from about 9 to about 15 carbon atoms.

14. The method of claim 10 wherein the quaternary ammonium compound is a pyridinium derivative of chloromethylated n-alkylbenzene, characterized further in that (1) the term pyridinium refers to derivatives of a mixture of pyridine and methyl-and-ethyl substituted pyridines, and (2) the n-alkyl portion of said n-alkylbenzene is a mixture of substantially straight-chain alkyl groups containing from about 9 to about 15 carbon atoms.

15. The method of claim 10 wherein the quaternary ammonium compound is a pyridinium derivative of a bis chloromethylated n-alkylbenzene, characterized further in that (1) the term pyridinium refers to derivatives of a mixture of pyridine and methyl-and-ethyl substituted pyridines, and (2) the n-alkyl portion of said n-alkylbenzene is a mixture of substantially straight-chain alkyl groups containing from about 9 to about 15 carbon atoms.

16. The method of claim 10 wherein the quaternary ammonium compound is a quinolinium derivative of chloromethylated dodecylbenzene wherein the dodecyl .portion of said dodecylbenzene is a mixture of branched- 15 chain alkyl groups containing from about 9 to about 15 carbon atoms.

17. The method of claim 10 wherein the quaternary ammonium compound is a quinolinium derivative of chloromethylated n-alkylbenzene wherein the n-alkyl portion of said n-alkylbenzene is a mixture of substantially straight-chain alkyl groups containing from about 9 to about 15 carbon atoms.

18. The method of claim 10 wherein the quaternary ammonium compound is a quinolinium derivative of a his chloromethylated n-alkylbenzene wherein the n-alkyl portion of said n-alkylbenzene is a mixture of substantially straight-chain alkyl groups containing from about 9 to about 15 carbon atoms.

References Cited by the Examiner UNITED STATES PATENTS 2,678,316 5/1954 Harris 260 290 2,759,975 8/1956 Chiddix et a1. 21 2.7 X 2,873,299 2/1959 Mikeska 260-651 2,945,894 7/ 1960 Earhart et al 260651 3,079,220 2/1963 BOieS et a1 21 2.7 3,079,221 2/1963 Anderson 21-27 3,107,221 10/1963 Harrison et al. 252-390 x 10 3,178,435 4/1965 Marxer 260--290 MORRIS O. WOLK, Primary Examiner. F. W. BROWN, Assistant Examiner. 

1. A METHOD OF INHIBITING THE ATTACK OF MINERAL ACIDS ON METAL SURFACES WHICH COMPRISES ADDING TO THE MINERAL ACID AN INHIBITING AMOUNT OF A SURFACE ACTIVE QUANTERNARY AMMONIUM COMPOUND REPRESENTED BY THE FORMULA 